The present invention relates to biaxially textured metallic substrates and articles made therefrom, and more particularly to such substrates and articles made by rolling and heat treating a metallic substrate to obtain biaxial texture, followed by deposition of epitaxial materials thereon, with an emphasis on superconductors.
Current materials research aimed at fabricating high-temperature superconducting ceramics in conductor configurations for bulk, practical applications is largely focused on powder-in-tube methods. Such methods have proved quite successful for the Bixe2x80x94(Pb)xe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O (BSCCO) family of superconductors due to their unique mica-like mechanical deformation characteristics. In high magnetic fields, this family of superconductors is generally limited to applications below approximately 30 K. In the Rexe2x80x94Baxe2x80x94Cuxe2x80x94O (REBCO), where RE denotes a rare earth element), TIxe2x80x94(Pb, Bi)xe2x80x94(Srxe2x80x94Ba)xe2x80x94Caxe2x80x94Cuxe2x80x94O and (Hgxe2x80x94Pb)xe2x80x94Srxe2x80x94Ba)xe2x80x94Caxe2x80x94Cuxe2x80x94O families of superconductors, some of the compounds have much higher intrinsic limits and can be used at higher temperatures and in higher magnetic fields. It has been demonstrated that these superconductors possess high critical current densities (Jc) at high temperatures when fabricated in essentially single-crystal forms as epitaxial films on single crystal substrates such as SrTIO3 and LaAIO3. These superconductors have so far proven intractable to conventional ceramics and materials processing techniques to form long lengths of conductor with Jc comparable to epitaxial films. This is primarily because of the xe2x80x9cweak-linkxe2x80x9d effect.
It has been demonstrated that in REBCO, biaxial texture is necessary to obtain high transport critical current densities. High Jc""s have been reported in polycrystalline REBCO thin films deposited on special substrates on which a biaxially textured non-superconducting oxide buffer layer is first deposited using ion-beam assisted deposition (IBAD) techniques. IBAD is a slow, expensive process, and difficult to scale up for production of lengths adequate for many applications.
High Jc""s have also been reported in polycrystalline REBCO melt-processed bulk material which contains primarily small angle grain boundaries. Melt processing is also considered too slow for production of practical lengths.
Thin-film materials having perovskite-like structures are important in superconductivity, ferroelectrics, and electro-optics. Many applications using these materials require, or would be significantly improved by, single-crystal, c-axis oriented perovskite-like films grown on single-crystal or highly aligned metal or metal-coated substrates.
For instance, YBa2Cu3Ox (YBCO) is an important superconducting material for the development of superconducting current leads, transmission lines, motors and magnetic windings, and other electrical conductor applications. When cooled below their transition temperature, superconducting materials have no resistance to direct electric current and carry electrical current without heating up. One technique for fabricating a superconducting wire or tape is to deposit a YBCO film on a metallic substrate. Superconducting YBCO has been deposited on polycrystalline metals or alloys in which the YBCO is c-axis oriented, but not aligned in-plane. To carry high electrical currents and remain superconducting, however, the YBCO films must be biaxially textured, with effectively no large-angle grain boundaries, since such grain boundaries are detrimental to the current-carrying capability of the material. YBCO films deposited on polycrystalline metallic or alloy substrates do not generally meet this criterion.
Goyal et al. have disclosed in U.S. Pat. Nos. 5,898,020; 5,958,599; and 5,964,966, as well as references disclosed therein, various inventions relating to preparing textured biaxial materials, the disclosures of the above-identified patents are incorporated by reference in their entireties. The method disclosed by Goyal et al. Is termed Roll-Assisted Biaxial Textured Substrates, or RABiTS, for short.
Accordingly, it is an object of the present invention to provide a new and improved method for fabricating elemental, alloy and laminated structures having biaxial texture.
It is another object of the present invention to provide a method of producing epitaxial superconductors on Ni, Ni alloys other face-centered cubic metals or alloys, and laminated structures having biaxial texture by practically scalable processes.
It is a further object of the present invention to provide vastly improved c-axis oriented, biaxially textured, superconducting YBCO films, or other perovskite-like materials, such as SrTiO3, reproducibly obtainable on biaxially textured Ni, Ni alloys other face-centered cubic metals or alloys or other metals on which an epitaxial buffer layer can be formed.
It is a further object of the present invention to provide c-axis oriented, biaxially textured perovskite-like ferroelectric films on face-centered-cubic substrates for metal/ferroelectric/metal multilayer devices.
A still further object of the invention is to provide new methods of preparing textured materials having less than 1% grain boundary misorientation angles greater than about 8xc2x0.
Further and other objects of the present invention will become apparent from the description contained herein.
In accordance with an aspect of the present invention, a biaxially textured elemental or alloy article includes a rolled and annealed biaxially textured metal substrate, the metal having a face-centered cubic crystalline structure, the biaxially textured substrate being characterized in that less than about 1% of grain boundaries have misorientation angles greater than about 8xc2x0.
In accordance with a further aspect of the present invention, a biaxially textured laminate article includes a rolled and annealed biaxially textured base metal substrate, the base metal having a face-centered cubic close-packed crystalline structure, having an epitaxial layer of another material on a surface thereof, the biaxially textured substrate being characterized in that less than 1% of grain boundaries have misorientation angles greater than about 8xc2x0.
Yet another object or aspect of the invention is to provide a novel process or method involving a combination of low and high temperature annealing to produce the articles described above.
A still further object or aspect of the invention is to provide a novel process or method of the type described using separate layers and small deformation steps.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.